Enamel coating for ferrous metals



June 15, 1943. A. E. CHESTER ENAMEL COATING FOR FERROUS METALS Filed June 25, 1941 Patented June 15, 1943 ENAMEL COATING FOR FERROUS METALS Allan E. Chester, Chicago, Ill., assigner to Poor & Company, Chicago, Ill., a corporation of Delaware Application June 23, 1941, serial No. 399,384

s claims. (c1. s-*48) This invention relates to a step in the process of enamel-coating ferrous metals involving the use of materials or bonding agents to control the amount er degree of thermal oxidation, and to provide for the rm adherence of the enamel coat to the metal, tlie invention primarily contemplating a new and useful bonding compound which includes vitrifiable ingredients, and having the practical quality of being used as a spray, like paint, in a single coat on the metal sheet to be enameled.

Further, the invention is particularly applicablelfor use with medium and low firing enamels,

as distinguished from those enamels of the art which function with cobalt, extensively employed in enameling procedure and which only functions at temperatures in excess of 1580 F. and which will not provide adherence or bonding when used with enamels .fusing below 1580" F., e. g., enamels which fuse in the range of approximately 1100o F. to 1460 F.

The invention therefore primarily has in view a new step in the process of enamel-coating ferrous metals which consists in subjecting the metal sheet, preferably a plain pickled metal sheet, as distinguished from a pickled sheet which has been subjected to an immersion deposition coating of nickel in a nickel ,sulphateboric acid bath, as disclosed in my companion application led June 19, 1941, Serial No. 398,842, to a bonding-glass compound carried in an aqueous-alcohol vehicle and employed as a spray which will insure complete dispersion of the compound over the metal surface, as Well as firm adherence of the same to the metal. To that end the invention contemplates the use of a bondingglass compound in which is combined certain essential ingredients or components permitting the same to be used as a single fired rustproofing coat on a metal sheet, or as the primer coat or base for a clear glass color coat superimf posed thereover when the metal is to be used for purposes other than merely for rustproong.

So far as known, the invention of the present desired, the primer coat, consisting of the bonding-glass compound carried i'n the aqueous-alcohol vehicle, is substantially dry. Furthermore,

lowering the surface tension of the slip, permits the penetration ofthe primer coat into serrations of the steel or ferrous metal, which results inthe formation of a flat smooth spray which enhances the smoothness of the surface' when the vitreous body is fused. v

The drawing is a diagrammatic {low-sheet indicating the special processing steps employed in preparing and developing the new bonding compound, preliminary to spraying the same as a spriming coat'on the metal sheet to be enameled.

In carrying forward the invention the new bonding compound, ground colloidally ine for spraying, is preferably made up according to the formulae and procedure as exemplified by the now-sheet drawing, to wit:-

It has already been pointed out that the present invention of the new bonding-glass compound is specially Vapplicable for use with plain pickled steel, and for illustrative purposes there is shown on the now-sheet a series of operations indicated by the numeral ,I which are conventional operations in the preparation of a metal or steel plate, preliminary to; having appliedvcompound the primary bonding ingredients are prepared according to the flow-sheet, namely, first, as indicated at 2,v a colloidal suspension is made of antimony trioxide and titanium hydroxide and wat-er, in the proportion for example.`

as given in the said block 2 of the flow-sheet.

This primary mixture is introduced into a ball mill, as indicated at 3, for thorough grinding, and

vthen the mixture of the primary bonding ingredients, from stage 3, is introduced into a drier as at I, following which nickel chloride, from a source of supply 5, is combined with the said ingredients in the proportions, as indicated at stage 6, of 100 parts by weight of said combined primary ingredients and 5 parts nickel chloride. Also, at the time of introducingth-nickel chloride into the said primary mixture following the grinding stage 3, there is incorporated in such mixture, to complete the bond compound per se.

- a specially prepared opacifying and oxidizing component from a source of supply. indicated at G on the flow-sheet. This special oxidizing component is a sodium zirconium silicate unusually high in alkali oxides preferably of the following formula, to wit:

This oxidizing component or agent of the above described formula, when introduced with the nickel chloride in the making of the bond compound per se, completes the formula thereof and the function of the sodium zirconium silicate, as a special oxidizing agent, provides, in the carrying out of the present invention, a rapid rate 0f thermal oxidation and a resultant fusion layer rich in ferrie zirconate and ferrie titanate which greatly increases the adherence of the coat or coatings to the metal sheet.

The above completed bond compound ormula is then carried to a dry mixer, as at "i, and at that stage the said complete bond compound is ready for incorporation in a mill formula i! consisting of a vitriable rustprooing composition which constitutes the complete bonding-glass compound.

Referring in detail to this mill formula, which includes two separate frit formulae a and b, a new and distinctive part thereof is the combination of a conventional frit, designated a as a hard member in a two component formula with a sharply defined eutectic composition, non-feldspathic and containingat least 27% barium oxide and 10.2% sodium uoride to provide the soft or uid member, designated b, which latter also "greatly increases the bonding or adherence of the fused. vitreous body to the metal surface. ,A typical example of the conventional frit a is as foll lows:

The said new frit formula b is of the following composition:

Parts by Parts by weight Feldspar 26.10 Borax 39.20 Silica 15.70 Soda ash 4.90 Soda nitrate 0.90 Fluorspar 8.40 Calcium carbonate 3.90 Bone ash 0.90

weight Barium carbonate 34.8 Sodium silica uoride 22.8 Boric acid 21.0 Quartz 10.8 Zinc oxide 10.6

As indicated on the flow-sheet the two' frit formulae a and b are respectively and separately carried through the stages of a dry mixer and smelted respectively at the temperatures of approximately 2200 F. for formula a and approximately 1900 F. for formula b. These two frit formulae are then finally brought together, asindicated on the flow-sheet. to form component parts of the aforesaid mill formula, which is preferably of the following composition:

Parts Frit Formula a 60.0 Frit; Formula b 40.0

Parts by weight Clay '7.0 Borax 0.2 Sodium zirconium silicate 6.0 Black oxide of iron 0.25 Bonding compound 2.1 Aqueous alcohol vehicle 40.0

It will be observed that at the point of compounding the above complete mill formula there is introduced into the same the above specified and important aqueous-alcohol vehicle :c of the following composition, as noted at 0 on the owsheet:

1 Parts by weight Water 91.266 Octyl sulphide .454 isopropyl alcohol 8.28

The foregoing additions complete the mill formula constituting the bonding-glass compound, and with all of the ingredients of that compound incorporated the same .is introduced into a ball mill at. stage 9 on the flow-sheet, where the same is ground to a degree of fineness preferably onehalf of one percent or less residue on a 200 mesh screen. Then the bondingg1ass compound is ready for use in a spray gun, as at step i0, for spraying onto the metal sheet a single coat of the said compound. the metal sheet with the single coat of the said bonding glass is to be employed as a rustproof product, it is desirable to give a brief drying at stage I i, in a suitable dryer or in the open air. The metal sheet is then subjected with its single coat to firing in' a conventional fusing furnace, as at stage l2, and with the formual of the coating as above given, the temperature of firing, at stage 32, is preferably within the range of 1350 F. to 3.400a F. The effect of the firing is to fuse the vitrinable elements of the bonding-glass, and to provide firm and uniform adherence of the finished enamel coat to the metal surface. The metal sheet thus provided with a single iinished enamel coat is ready for use, as indicated at stage i3 on the flow-sheet, as a finished rustproof product.

It has already been pointed out that in'cases where it is desired to provide the coated sheet with a decorative color, that is, with a colored enamel finish, it is only necessary before drying the coated metal sheet to superimpose, on the rst or single coat of the bonding glass, a clear glass color-coat, that is, a glass or frit having no adulterants nor bonding ingredients. The provision for this second enamel color-coat is indicated in the diagram of the flow-sheet where, at step I4, is indicated the use of any conventional clear frit or glass composition usable with colors, which composition is. prepared in the usual way in a smelter, as at step l5, and the frit, following the smelting operation of the clear glass composition, is combined in an enamel color formula, for example:

This enamel color formula, indicated at step I6, of the supplemental coating steps is introduced into a ball mill grinder, indicated at step I1, and the mixture ground to 1% or less residue on 200. mesh screen, after which the enamel color mixture is sprayed as a separate coat, as at step I8 on the flow-sheet, directly upon the primer coat of bonding glass, at step III, as indicated by the dotted arrow |85. g sheet is subjected respectively to the drying stage I I and to the ring or fusing stage I2, and the resulting product, as indicated at step I9 of the flow-sheet, becomes a finished one-red colored enameled product, not only having rustproofing qualities but valso usable for decorative purposes.

A variation of the process as described maybe resorted to with advantageous results where .cer-

tain conditions in an enamelng plant, such as aqueous-alcohol vehicle y composed of Parts by weight Water 91.266 Octyl sulphide .454 Butyl alcohol 8.280

In other words, in the variation of the process employing the aqueous-alcohol vehicle y there is merely a substitution of butyl alcohol for the isopropyl alcohol heretofore referred to, and an equivalent of these two alcohols that may be substituted therefor is diethylene glycol mono butyl I ether. `In all other respects all of the formulae and the procedure are the same in providing either the single enamel rustproongicoat for the metal sheet, or the two-coat colored enamel sheet, as already described.

In the method described the temperature em-A ployed for firing the coated metal is much lower than that employed in the conventional sheet Then the thus double coated metal enamel processes, thereby permitting the invention to be carried out i1.- connection with lighter gauge metal sheets than heretofore possible.

From the foregoing description it is thought that the essentials of the inevntion are fully defined, but it will be understood that any modications or alterations in details of procedure, or in the proportion of parts employed, falling Within the scope of the appended claims may be utilized. without departing from the spirit of the invention. I

l 1. .A coating composition for use in enamel coating processes, consisting of a mill formula including an aqueous alcoholvehicle, a bonding compound having a base of antimony trioxide and titanium hydroxide and including sodium zirconium silicate, and a blend of a, raw glass batch oi' relatively high maturing temperature with an eutectic frit of a relatively low maturing. tem,- perature.

2. A coating composition, for use in enamel.

titanium hydroxide, nickel chloride and sodium zirconium silicate, and a blend of a raw glass batch of relatively high maturing temperature with an eutectic frit of a relatively low maturing temperature.

ALLAN E. CHESTER. 

